Ian D. Longley, M.W. Gallagher Particle and sensible heat fluxes measured by eddy covariance above and within an urban canopy Ian D. Longley, M.W. Gallagher School of Earth, Atmospheric & Environmental Sciences, University of Manchester, UK Presented at the 6th International Conference on the Urban Climate, Göteborg, 2006

Particulate emissions from cities Biosphere impacts Climate impacts Regular emission cycles Sheltering, recirculation, deposition, inversions Within urban canopy: Direct impacts on human health Advected air is relatively clean Emission from surface following relatively predictable cycles Net emission from city has downwind impacts – direct radiative, CCN and hence indirect radiative, biosphere impacts on deposition Physiochemical nature depends upon physiochemical nature of emissions & timescales Recirculation and trapping in UCL

PM10 emission inventory (UK NAEI) tonnes km-2 a-1 Above: all sources Below: road transport (48% of total) No information on composition or size distribution No temporal information No experimental verification Current emissions quantified on 1km x 1km grid estimates of PM10 (mass of particles below 10 microns). Values reported are tonnes / km2 / year. No information given on temporal variation.

Ultrafine particles Above: mass size distribution from Princess Street, Manchester UFP toxico link Coarse increasingly important as UFP tackled, and in terms of mass, health effects not insignificant Above: number size distribution from Princess Street, Manchester

CityFlux University of Manchester Centre for Ecology & Hydrology (UK) 2004-7 Pilot study: Manchester June - July 2005 Direct measurement of particle fluxes from city centre by eddy covariance

Manchester, UK 50 km inland 2.5 m population High density core zH ~ 20 m 50 % PM10 from road transport Trips into centre: ~ 50 % car, 50% public transport Very little vegetation in core

CityFlux – Manchester (UK) – July 2005 Canopy/Canyon sites: Tower site: Portland Tower (90 m) 1. UoM 2. Deansgate

CPC (Eddy Covariance) Flux system u,v,w Dorsey et al., 2002, Atmos. Environ. 36, 791-800. N (Dp > 17 nm) cm-3 40 lpm

Total particle number and sensible heat flux Mean particle flux: 27 300 cm-2 s-1 or 28 800 cm-2 s-1 (upward only) 29 900 cm-2 s-1 (upward only) Stockholm (Mårtensson et al., 2005) Deposition rare Approximately log-normal distribution of 10-minute average particle fluxes

Mean diurnal fluxes See also poster by Martin et al. Above: Mean diurnal fluxes at 90 m Above: diurnal mean traffic volume in subject street canyon Above: Diurnal mean concentrations at 2 and 25 m Mean sensible heat flux = 106 W m-2 Some hint that ventilation velocity is positively related to u* and is enhanced in unstable conditions Sunrise 05:00, Noon 13:15, Sunset 21:20 local See also poster by Martin et al.

Canyon roof level (Maybrook House, Deansgate) Highly complex flow with large and variable degree of sheltering

Conclusions Particle number fluxes were measured at 90 m above central Manchester Fluxes had a clear diurnal cycle, with peak in early afternoon - very similar to that for sensible heat flux These results very similar to Edinburgh 2001 Sensible heat fluxes at canyon roof level very similar to 90 m, although decay in afternoon was more gradual

Forthcoming analysis Spring/Summer 2006 Winter 2006 data (poster by Martin et al.) Influence of stability Model for particle ventilation fluxes Prediction of urban canopy concentrations Spring/Summer 2006 Continued measurements at Portland Tower, including size-segregated fluxes Multi-level compositional measurements by AMS Tracer release to identify source-receptor relationships and transport timescales

And GVA Grimley for kind permission to use Maybrook House Acknowledgements Many thanks to Bruntwood Properties for kind permission to use Portland Tower And GVA Grimley for kind permission to use Maybrook House

Mean number flux as function of wind direction 40 000 20 000

PM10 emission inventory (NAEI) Above: all sources Below: road transport (48% of total) PM10 inventory gives no clear clues as to enhanced sources in WNW

Local WNW sources? Portland Street Princess Street Construction sites

Chinese cooking? But low fluxes on Sundays

Mean diurnal particle fluxes (evening peak) Sunset at ~ 21:20 local time WNW is prevailing wind direction in June & July Peak in diurnal cycle in evening associated with WNW winds. Check every day – did evening peak occur? Frequency of WNW winds peaked in late evening Second evening peak always and only seen in WNW winds Mon-Sat

Street canyon particle concentrations and composition Above: time series of particle composition mass loadings from Aerosol Mass Spectrometer (AMS) Above: diurnal mean traffic volume in subject street canyon 25 m level will more closely resemble ‘urban background’, i.e. workplace (and some residential) exposure Above: diurnal mean particle number concentrations (DMPS) at top and bottom of street canyon Above: Diurnal mean of particle composition mass loadings from AMS

Urban Particle Numbers Particle number concentrations dominated by ultrafines Above: mass size distribution from Manchester street canyon Above: number size distribution from Manchester street canyon Longley et al., 2003. Atmos. Environ. Particle toxicity appears to lie in ultrafine fraction Traffic is the dominant urban source, but emission factors poorly quantified